ASTRONOMISCHE NACHRICHTEN. IT 3771. Band 158. 3-

The Nebula about Nova Persei 1901 9. By 1;: W. Very. In a letter to the Editor of the Astr. Nachr. No. 3736 *esemble those of a series of explosions produced by a dated Aug. 23, 1901, MM. Flammarion and Antoniadi an- brce of gradually waning energy. nounced the discovery of a nebulous aureole, 6' in diameter, The following considerations prove, however, that the around Nova Persei 1901. Dr. Max Wolf immediately con- nebulous streaks are not portions of spiral streams emanating firmed this observation, and, in addition, recorded a further from the star under the action of any ordinary hydrodynamic extension to a distance of 5' from the nova, at least on pressures. Great mass would be needed in this case to the south side and somewhat to the east, the nebuloiis prevent the dissipation of the star simply by the centrifugal material being excessively faint, and yet rich in structure. force of rotation. A body having a mass 1500 times as Although these early observations have been questioned on great as our sun's and a diameter of IOOOOOOO miles could the ground that the aureole may have been only an instru- rotate once in 2 hours without generating an equatorial mental effect, due to the preponderance of ultraviolet light surface -motion greater than the parabolic velocity, but some in the rays from this star, and to the use of an imperfectly such speed of rotation would be needed to produce spiral corrected telescope, the reality of the more extensive streamers by combination with the radial velocities spectro- appendage and its nebulous character have now been com- scppically observed ; for the spectrum of Nova Persei I 90 I pletely confirmed from photographs with powerful reflecting exhibited at the violet hydrogen line (HI, displacements telescopes at the Yerkes and the Lick Observatories. of 30 tenth-meters, which, if due to motion in the line of The nebula photographed by Mr. Ritchey 2) has every sight, correspond to a mean velocity of 2193 km, or 1363 appearance of being concentric with the star and an ap- miles per second. A radial movement of this amount, en- purtenance of that body. It also has a structure which is during unchanged for 210 days, from the appearance of either spiral, or composed of several annuli, or fragments the star, February 22, to the date of Ritchey's first photo- of annuli, probably lying in different planes and thus seeming graph, September 20, 1901,should carry the erupted gases to intersect. The outer parts of the nebula are strongest to an extreme distance from the star of 3.98 x (10)10 km. on the southern side where they consist of parallel or con- The radius of the nebula, as photographed by Ritchey, is centric segments about apart. On the following side, about 480", whence I" = 82900000 kilometers, and the in the September photograph, there are four concentric parallax (on these assumptions) would be 1180. Dr. Cour- segments of annulli, or perhaps of spherical shells, about voisier of Heidelberg has published meridian-circle observations xlf2' apart. (A. N. 3753) which prove that the parallax of the nova is To see if it would be possible to account for these certainly less than of a second of arc, and in the United features on the supposition that they are remnants of stellar States, Messrs. R. H. Tucker and R. G. Aitken of the Lick envelopes thrown off by periodical hydrogen eruptions, I made Observatory, and Chase of New Haven have each arrived some preliminary computations with various assumptions. at the same conclusion independently. Consequently the Father Hagen 3) has given a light-curve of the nova nebulous streamers cannot have been produced directly by from a compilation of the results of many observers, which explosive outbursts of hydrogen. To form the outer annulus indicates that at the beginning the period of luminous variation shown in Mr. Ritchey's photograph of September 20 at a may have been as short as I day, and that it afterwards distance of 7 to 8 minutes of arc, a mean radial movement increased rapidly to a mean period of about 3 days, which of I' in 4 weeks would be required. Comparison with Dr. has now further lengthened to 41l2 or 5 days. Wolf's observation indicates an outward or expansive motion The concentric structure on the outskirts of the nebula also of I' in the same time on the south side, if we assume on the southern side, which by supposition has been first that both measurements relate to the same nebulous detail. produced, is much finer, that is to say, the streaks are closer Perrine's observation of a motion at four different points together than those nearer the center, and as if pertaining in the nebula, which he has been able to identify with to operations in a more rapid sequence. The phenomena structures shown in Ritchey's first photograph, through one

l) Read at the fourth annual meeting of the Astronomical and Astrophysical Society of America. Dec. 31, 1901. z, 'Astrophysical Journal, vol. 14, plates XVIn and XIX, November, 1901. s, Rev. J. G. Hagen, S. J. .Preliminary Light Curve of Nova Persei 1901. From February 22 to May 1.a Georgetown College Observatory Circular. 3 35 37 I 36 and one half minutes of arc in fortyeight days, demonstrates lot less than of a second of arc, and its maximum a velocity of the same order, which is further confirmed by %stance not over 124 light-years. Its parallax ought, there- Ritchey's photograph of November I 3. bre, to be within the range of possible careful measurement. Mr. Ritchey finds that the entire southern half of the All novae that have appeared up to the present time nebula has been expanding rapidly and nearly radially. lave been associated with the Milky Way. If it be admitted Perrine's observations differ slightly. >The displacementsc ihat Nova Persei is a constituent member of the galactic he says ,agree well.. . .The directions are not so consistent, jtream, we have now, and for the first time, an approximate and could perhaps be explained by irregular niotions in the dea of the distance to the Milky Way which, in the con- nebulous mass. c Mr. Ritchey's later photograph shows that stellation Perseus, cannot be more than about IZOO million careful discrimination will be needed to distinguish changes million kilometers away. of shape in minor details from general movements. It appears probable that like the tails of comets, the The fact of motion in nebulous matter is thus abund- ,urninous bodies of the gaseous nebulae require only a small antly demonstrated, but it is equally certain that this motion miass of excessively diluted material to produce their shining. is not that which we have been seeking, and due to explosive eruption of gases in large masses. It is rather to an electric repulsion of individual atoms or corpuscles, similar to that Let us now examine the evidence to be deduced from which gives the cathode rays in a Geissler's tube, or perhaps :he spectroscopic measurements. The structure of the hy- to motions initiated by that pressure of light which has now drogen bands in the spectrum of the nova has exhibited been demonstrated by the experiments of Nichols and Hull, great complexity and variability. In general, each band has that we must look for an explanation of the rapidly growing been found to consist of a broad region of absorption on and fast fading nebula. The annuli may be gigantic striae the violet side, with local intensificatibns of absorption, or similar to those seen in electrified tubes containing rarefied dark lines, which are repeated in the same order of position gases, and may be produced by chemical combination of or intensity in nearly all of the bands. The half towards different sets of atoms or corpuscles, thrown off during the red end of the spectrum is always bright, and has been alternating phases of the eruption, and electrically or lumin- commonly subdivided into from two to four or more minor ously repelled at different speeds depending on the nature bands, separated by absorption lines in the same relative of the particles; or if spiral motion should be certaidy positions in every one of the hydrogen bands, with trifling indicated, we may surmise that there has been some sort exceptions which may be explained by the superposition of of cathode discharge along, or (more accurately) around spectral lines of other substances. The displacements of magnetic lines of force. similar subdivisions, according to the measures of Campbell Professor J. J. Thomson 1) has found that the speed and Wright, are proportional to the wave-length, and are of the electric discharge, when striae are produced, approaches consequently due to motion in the line of sight; and each that of light. Although no such velocity is implied for the subdivision of a band must be attributed to light emanating atoms in vacuum tubes, it is possible that, in free space, from, or absorbed by the atoms of an individual gaseous electrified particles of less than atomic dimensions, namely, mass or stream having a particular velocity in the line of sight. those Thomsonian corpuscles which appear to constitute The gathering of the principal dark subdivisions on the very substance of static electricity, may exhibit velocities the violet side, and of the bright components on the red of this order. Assuming the velocity of light as an outside side of each band, without any exception, may all be ex- limit for the speed of particles thrown off from the nova plained as due to the presentation of successive shells of by electric repulsion, it follows that the parallax of Nova hot gas, periodically expelled from the star, and arranged Persei I 90 I , corresponding to the dimensions of the bound- concentrically around it. The receding half of each shell ary of Ritchey's nebula, cannot be less than of a presents its concave and hottest internal surface toward us, second of arc. and the radiation from these receding masses has its wave- At the Washington meeting of the Astronomical and frequency so much diminished by the backward linear motion Astrophysical Society of America, Professor Campbell an- that its bright lines lie in parts of the spectrum where the nounced the discovery by Perrine of a fainter nebulosity hydrogen on the nearer side of the star has no absorptive about the nova, having a circular form and extending to power a). Hence the light from the receding streams has twice the diameter of Ritchey's nebula. This, according to great brilliancy. The approaching shells of erupted gas, on the hypothesis under discussion, points to a broad division the contrary, present their outer and cooler surfaces toward of the emitted particles, those of one kind having just half us. The radiation of the deeper and hotter layers of ap. the density of the others, and traveling twice as far under proaching gas is consequently absorbed by the hydrogen of the action of the same forces. Since there is no example outer and comparatively cool layers appr.oaching at similar of motion of material particles, either actual or apparent, speeds and absorbing in the same spectral region. M. Des- exceeding the velocity of light, we may still take this landres (C. R., vol. 132, p. 620, 1901) has recorded three velocity as a limiting one, and, in accordance with what such local absorption lines within each dark hydrogen band, precedes, must conclude that the parallax of the nova is denoting velocities of approach of I zoo, 1600, and 1850km

') Philosophical Magazine (s), vol. 30, p. 129, 1890. ') This suggestion has been made by Professor W. H. Pickering. Astronomy and Astrophysics, 101. 13, 1). 201, 1894. 37 3771 38 respectively. Campbell and Wright (Lick Obs. Bull. No. 8, )osition of the Hd line is at wave-length 4101.85 tenth- Sept. 12, 1901) also record these lines. To the strongest a neters, where its position and ditnensions are shown in displacement at Hi of -20.5 tm. is assigned, corresponding he figures. to a velocity of approach of 1499 km. The interpretation of these light-curves which I wish The many variations which have occured in the spectrum o suggest, is founded on the supposition that the phenomena of the nova would require a large volume for their description; ire due to the formation of successive spherical shells of but for the understanding of the processes involved in their ncandescent hydrogen, and to their expulsion from the star production, the behavior of the hydrogen bands is most >y a series of rhythmical explosions with intervals of rest. noteworthy. Fig. 3 is a section of such a shell after expansion Fig. I. and just before the production of a new shell. The earth 3eing in the direction of the arrow, the positions of luminous a Ir matter at a b a' b', lying on a circumferential zone at right angles to the line of sight, furnish a large part of the light, and are also moving so nearly athwart the line of sight as to give spectral radiations but little deviated from the normal frequency. The half of the zone nearest to us (a a') produces bhe stronger part of the band on the violet side of the normal position of Hi; the more distant part (b b') gives the second maximum on the red side ; and the intermediate depression is due to the absorption exercised by the cooler, but still incandescent gas on the outside of the shell. As this absorption chiefly affects the radiation from the more

Fig. 3

4050 4100 4 /SO Two types of these bands may be singled out as especially significant. Rev. Walter Sidgreaves of the Stonyhurst College Observatory was, I believe, the first to point out (Astroph. J., vol. 13, p. 278, May, 1901) that the distribution of light in the hydrogen bands was symmetrical at the time of a minimuni (Fig. I), but unsymmetrical at the epochs of maximum luminosity. I choose as an example of the last a Lick Observatory light-curve (Fig. 2) obtained July I, 1901, because it shows a great deal of structure on the red side

Fig. 2. < et distant side of the zone, it may be indicated symbolically by the expression (b - a) without, however, attaching any rigid algebraical meaning to the signs. The progressively fainter extensions of the band, c, d, are from the thinner sections of the shell to which the same letters are attached. The areas and the sectional depths of normal zones presenting equal angular widths, diminish as the line of sight is ap- proximated. The light from these zones is therefore fainter, and the deviations from the normal position of the spectral line are progressively greater as the rays are emitted from parts of the shell nearer to the intersection with the line B of sight through the star. The radiation from the hydrogen

r/- I at d, as already explained, is not absorbed in passing through 4 050 4 i00 the hydrogen at c, because of its different periodicity. Fig. 4 is a section through the system at the maximum of the band, but I cannot think that it differs essentially of the light period. A second shell of hydrogen has been from earlier examples of the type, less rich in structure, emitted, hotter than the now much expanded previous shell. where possibly a superfluity of minor details has obscured The zone e f e'f, gives a broader emission band, because the pattern. Fig. I is for the 5th of April. The undeviated embracing a wider range of velocities in the line of sight 3" 39 3771 40

cities in the line of sight as the distance from the star in- creases. The outer layer (3) was also the coolest, since its absorption line had the greatest intensity. The phenomenon disappeared after March 28, 1901, according to Mr. Adam [loc. cit., p. 161). Now in its earlier history the nova gave evidence of B short light-period (about I day) possibly superimposed on a longer, or 3 -day period. Let it be assumed that the dark lines may be referred to shells emitted in the shorter period, and that the slowing of the radial velocity of the successive shells is due to control by the attraction of the central mass. This mass may be approximately determined. The spectral displacements given correspond to velocities in the line of sight and to distances attained with these velocities in one, two, and three days, as follows:

Velocity Distance than obtains in the zone shown in Fig. 3. The deep de- pression formed by the absorption of the outer and cooler 284 x (IO)~ layers of e f e’fr is partly filled by the radiation from the zone a b a‘ 6’ of the outer shell, making a band both nar- The diminution of the solar parabolic velocity between rower and fainter thau before, because of lower velocity these extremes of distance is only 9 miles, as compared and temperature. The radiation from ff’ does not equal with 305 miles for the nova, whence it follows that the that from e e’, because partly absorbed by the hydrogen in mass of Nova Persei 1901 must be about (33.9)2 = 1149 the latter, as the periods are not sufficiently different tc times the mass of the Sun, confirming the suggestion that prevent some overlapping of spectral regions appropriate tc stars having explosive properties are of exceptionally great the two sources. The radiation from R is not thus affected mass. With such a mass, it is easy to believe that phenomena since it is optically outside the limits of the zone e f elf’ of uncommon magnificence, bearing witness to a display of and of different periodicity from the hydrogen at g and c enormous energy, have resulted from disturbances on so through which the rays froni R have to pass. Hence tht grand a scale. radiation from h equals or surpasses that from e f e’ f’ whicf It seems to me that these facts throw light upon the would otherwise be much more intense. The radiation from origin and significance of the nebula which probably do g, on the contrary, is greatly absorbed by the hydrogen a not play the role assigned to them by Laplace, but which c which possesses nearly the same velocity and periodicity must be distinguished into true nebulae and gaseous bodies. To this is due the lack of symmetry of the bands at thc The latter are to be likened rather to the tails of comets, maximum, or double-shell epoch. The inner shell has i and are perhaps, like them, appendages perpetually reproduced somewhat greater radial velocity than the outer shell, henci from sources whose disposition alone gives fixity to the radiations from g and h produce slight extensions of thc nebulous phantom. It has also been shown in what precedes edges of the band beyond the limits of the superposed ban( that immediately about the nucleus of the nova, there are due to rays from c and d. probably concentric shells of gas resembling the multiple The total extent of the violet hydrogen band (Hd concentric comae of some of the comets, and that the according to Mr. Walter S. Adams (Astroph.J., vol. 14,p. 164 spectroscopic and visual motions belong to phenomena of Oct. 1901)was frotn 24067 to R 4146, with the center a entirely different orders. 4 I 05 tenth-meters. It seems probable that the preparation for a nova is In the earlier history of the nova, fine dark absorptioi of very long duration, and that long before its appearance, lines appeared in the same relative positions on the violet sidl of all of the hydrogen bands in the region of the unsym the nova has been a single body of great mass and con- siderable central condensation; also that it has previously metrical absorption on the violet edge, which had its chie been intensely hot at the center, but surrounded by clouds intensity for the Hd band at 4082. The accurate wave 1 of discrete meteorites, which had not yet coalesced with lengths of three of these lines are given for the group a the primary in its antecedent condensation, and wich have Hd on March 18 by Campbell and Aitken as follows: prevented its appearing as a luminous body, until at last (I) Faintest 1 4074.6 Displacement -27.3 the pent-up internal forces have burst their bounds and (2) Stronger 14077.4 > -24.5 have dissolved the last remnants of obstructing matter in a (3) Strongest 14081.3 > -20.6 final blaze. These lines bear witness to an absorption at this time b In this instance there does not seem to have been three concentric shells having progressively diminishing velc any large loss of substance by the explosive eruptions of gas. 41 377' 42

The nucleus still retains its great mass," and the variation remote epoch in the future, although perhaps never again of luminosity in a more than centesimal ratio is evidence after the manner of the original appearance of the nova. that no conclusion can be drawn from the brightness of In conclusion, I desire to subscribe to the opinion the star as to its actual mass or size. The fading of the of Professor Cleveland Abbe, as expressed by him in the continuous spectrum is perhaps due to a reprecipitation of Monthly Notices of the Royal Astronomical Society for I 86 7, clouds of cosmic dust after the first outpouring of intense (vol. 2 7, p. 2 5 7) that the true nebula are galaxies, or complex radiation and highly heated gases has dispersed the super- aggregations like our own Milky Way, *and are >composed fluous energy. If so, we may anticipate a gradual recuperation of stars (either simple, multiple, or in clusters) and of of forces, and a possible renewal of luminosity at some gaseous bodies of both regular and irregular outline. a Arcturus, Virginia, January 1902, Frank W. Very.

Beobachtungen der Nova Persei (Ch. 1226) auf der Sternwarte Jedrzejewicz in Warschau, von B. MerecKi. Die Grossenmessungen wurden mittelst eines Keil- Zahl der BD. Grosse Beob.-Tage photomers am Cooke'schen Refractor von I 4 cm Oeffnung ausgefuhrt. Zur Verification der Constante des Keilphotometers +43"32 79128 8 und zur Reduction der Nova wurden a, 6, v, 30 und 84 (Heis) +43.766 8.22 5 Persei benutzt, wobei die Constante in der Regel aus Be- +43.730 6.84 5 obachtungen von zwei oder drei der genannten Sterne be- 4-44.734 6.45 5 stimmt wurde, wahrend einer von denselben zur Reduction -1-43.739 8.96 2 der Nova diente. Es ist hinzuzufiigen, dass die Constante, BD. +44?734 ist 84 (Heis) Persei. abgesehen von atmospharischen Verhaltnissen und der Hellig- Eine Correction wegen der atmospharischen Extinction keit des Himmelsgrundes, nur unbedeutenden Aenderungen wurde nicht angebracht. unterlag, wahrend auf sie die Grossen der Vergleichsterne Die ungiinstige Lage des Beobachtungsortes erlaubte selbst weit grosseren Einfluss hatten. die Messungen der Nova nur bis zum 3. Mai fortzusetzen. Vom April an wurden die Beobachtungen in der Dam- Die Grossenschiitzungen der Sterne a, d, 30 und 24. v, merung am hellen Himmelsgrunde ausgefiihrt. Nach zwei- 84 (Heis) Persei sind nach G. Muller und P. Kempf (Astr. monatlicher Unterbrechung wurden die Messungen am Juli Nachr. 37 14) angenommen. 14. wieder aufgenommen. Wegen der grossen Zahl der in Perseus neuentdeckten Die Beurtheilung der Farbe der Nova (seit April 18) veranderlichen Sterne, habe ich im August einige Sterne, bezieht sich auf ihr Scheibchen; ilbrigens war bis Mitte die als Vergleichsobjecte besonders bequem zu sein schienen, August ein rother Strahl fortwahrend bemerkbar und desto photometrisch untersucht und ihre Griissen nach 30 Persei deutlicher, je naher die Nova dem Horizonte stand. Im bestimmt; es zeigten sich dabei in einigen Fallen ziemlich Steinheil'schen Objectiv zeigte sich der rothe Strahl auf- grosse Differenzen zwischen den von mir erhaltenen Grossen fallender, als im Objectiv von Cooke; dieser rothe Strahl und denjenigen, welche Hagen fur sie gegeben hatte. Ich ist jedenfalls ganz verschieden von der bekannten Farbung habe namlich folgende Werthe bekommen : der Sterne, die die Dispersion in der Atrnosphare verursacht. Im folgenden Verzeichniss ist in der dritten Columne bei a, 6, -v, 30 zu erganzen:- Persei, bei 84: Heis Persei. M. 2. 1901 M' '' I Nova Bemerkungen 1901 Nova 3osse Bemerkungen Warsch. aarsch. __ I Febr. 27 9h'3" a -om13 2mo413 weissgelb April 6 8h 15~v +1m17 5m20 Marz gelbroth +1.88 3 8 48 a +0.44 2.61 4 6 9 4) v 5.91 blutroth 7 82a +1.14 3-31 3 roth 6 9 4J d +2.62 5.94 I2 826 4-0.33 3.65 3 blutrot h 6 10 4 6 4-2.74 6.06 I0 blutroth 13 8 6 +0.94 4.26 3 7 8 50 V +2.39 6.4 I blutroth 15 806 +1.04 4.36 I gelbroth 7 9 50 v +1.76 5.79 17 8 22 6 +0.76 4.08 2 blutroth 8 8 I1 v +1.52 - - - 5.55 29 8 30 gelb, rother Strahl I1 9 20 v +2.00 6.03 gelbroth 30 926 +1.62 4.94 4 gelb, etwas rothlich 14 93v +1.85 5.88 gelbroth 8 6 +r.50 4.82 etwas rothlich 18 v +0.23 4.26 gelbroth 3' 23 9 47 - April I 80d +1.13 4.45 gelb '9 9 30 - '1 5 9 '5 d +1.60 4.92 gelbroth 22 90v +1.62 5.65 gelb

l) Wolken. v Persei mit blossem uge sichtbar; Nova nicht.